The invention relates to single stage power factor correction (PFC) converters and in particular, the invention relates to a single stage PFC converter, in which some energy is transferred directly from the rectifier output to the converter output.
There are a number of standards which specify the requirement of the line current harmonics of electronic equipment. In order to meet those standards, the active power factor correction circuit is demanded.
The typical prior art approaches for meeting these harmonic standards are set forth in the patent literature as follows:
U.S. Pat. No. 5,434,767 to Batarseh, et al.; U.S. Pat. No. 5,636,106 to Batarseh, et al.; U.S. Pat. No. 5,844,787 to Fraidlin, et al.; U.S. Pat. No. 6,266,256 to Lehnert, et al.; and, U.S. Pat. No. 6,044,002 to Van Der Wal, et al. are each without an additional winding connected to the rectified input side and not arranged to transfer to the output directly during the time when the line voltage exceeds a preset value.
Also of background interest are: U.S. Pat. No. 5,508,903 to Alexandrov, et al.; U.S. Pat. No. 5,903,446 to Huillet, et al.; and, U.S. Pat. No. 6,097,614 to Jain, et al. although each of the three is to a DC/DC converter (not for a PFC AC/DC converter); and, finally U.S. Pat. No. 6,046,914 to Lauter uses an additional winding connected with the boost inductor as a voltage feedback sensor to alleviate the voltage across the bulk capacitor.
It appears from the prior art teachings known to the inventors that the present approach for meeting the standard requirements of the line current in low cost and low power applications is the common scheme of a single stage power factor correction circuit. The typical characteristics of such single stage PFC schemes include:
1) Combining a power factor correction (PFC) cell with an isolated DC/DC conversion cell; and,
2) Two PFC cells share one main power switch and one simple controller.
The typical prior schemes suffer from high direct current (DC) bus voltage stress, low efficiency and/or high output ripple, since all energy is firstly transferred from line source to DC bus storage capacitors by PFC cell, and then transferred to the load by a direct current to direct current (DC/DC) conversion cell.
It is the object of this invention to provide an improved single stage PFC scheme.
It is a further object of this invention to provide an improved single stage PFC scheme with higher efficiency.
It is another object of this invention to provide an improved single stage PFC scheme with active DC bus voltage control.
According to the invention, there is a power factor correction alternating current to direct current (AC/DC) converter comprising: a power factor correction cell having two AC input terminals, a transformer, a switch and two DC output terminals; a DC-DC converter cell having two DC input terminals, inductor, transformer, switch and DC output terminals; a duty cycle controller having an output voltage sense and pulse width modulation cell; and, means for transferring a portion of the power from said PFC cell directly to its output.
Other features, objects and advantages of the invention will become apparent from the following detailed description when read in connection with the accompanying drawings.